Thermo-Electric Cooling (TEC) devices are generally based on thermo-electric (TE) heat pumps (e.g. solid-state active heat pumps) that use electrical energy to pump and transfer heat from first region(s) of a device to second region(s).
TEC systems are generally characterized by improved pumping performance, such as greater temperature differences obtainable between their “hot” and “cold” regions and higher cooling rates per unit area, in comparison to other cooling techniques. The solid state nature of TEC systems (no moving parts, maintenance-free), as well as their improved pumping performance make them highly suitable for controlling the operation temperatures of many kinds of electronic devices, the proper operation and/or operational properties of which are dependent on their temperature conditions. These include electronic and solid state based devices, as well as optical and electro-optical devices. Also, in certain laser systems maintaining stable temperature it might be essential to stabilize the output frequency of the laser, for which TEC system can be used.
FIG. 1A illustrates schematically a typical configuration of a TEC system 130 thermally interfacing, through a surface S1 (e.g. being the surface of a heat spreader 120 and/or thermal conductive coupling materials 160), with an electronic device 110 to be cooled, i.e. from which heat should be evacuated. Also, TEC system thermally interfaces through another surface with a heat sink structure 140 for efficient heat exchange with the environment. Utilizing such TEC device for the purposes of heat evacuation from the electronic device 110 (e.g. heat-generating device) enables to maintain/control a working temperature TS of device 110.
The TEC device should pump heat at a heat rate dQP/dt (Qp being the heat pumped by the TEC and t being the time) greater or at least equal to the sum dQS/dt (QS being the heat generated by the device-to-be cooled) of the heat generation rate of the device 110 and the rate of heat flow from the environment to the device 110 (e.g. due to difference in their temperatures). The achievable heat pumping rate dQP/dt of thermo-electric heat pumps typically increases with the dimensions of the surface S2 of the heat pump through which heat is pumped, and decreases with an increase in the temperature difference (against which heat is pumped) between the ambient temperature TE and the temperature TS of the device-to-be-cooled 110.
In some cases, for given ambient temperature and operational temperature of the device 110, the heat flux (dQS/dt)|S1| through the surface(s) S1 of the device 110 is greater than the possible maximal heat flux (dQP/dt)/ds achievable by thermo-electric heat pump (e.g. through the surface S2). Then, pumping and evacuation of the heat generated by the device 110 can be achieved by utilizing a thermo-electric heat pump 135 having a larger heat pumping surface S2 and a heat spreader 120 for spreading the heat emitted through surface S1 onto the larger heat pumping surface S2.
The amount of heat flux that can be evacuated/pumped from a given surface S1 by utilizing a single thermo-electric heat pump 135 under given ambient conditions (ambient temperature TE) is limited, and accordingly the achievable temperature difference ΔT between the ambient temperature TE and the temperature TS of the device to be cooled is also limited. This is mainly because of the following: as the temperature difference ΔT increases, an increase in a natural heat flow between hot and cold regions occurs in a direction opposite to the direction of the heat pumping, and the efficiency of heat spreaders at concentrating heat pumping rates (e.g. from a relatively large thermo-electric heat pump (surface S2) to a smaller device (surface S1) from which heat is to be pumped) is also significantly reduced as the ratio of concentration (S2/S1) increases. Typical temperature difference ΔT between the cold side (first region) and hot side (second region) of a TEC of this type is limited to about 30-70° C. If larger ΔT is required, the hot side of one heat pump of the TEC may be cooled using another heat pump in the so-called cascaded configuration of the heat pumps. In such two-pump configuration of the TEC, the achievable ΔT of the entire TEC is larger (but not twice) than that which might be achieved by a single heat pump.
Known cascaded TEC devices typically include 3 or 4 heat pumps. The cascaded arrangement is typically aimed at providing large ΔT (e.g. maximal temperature difference) between the hot side and the cold side of the TEC.
An example of typical TEC device 130′ comprising two cascaded heat pumps (e.g. thermo-electric) is illustrated schematically in FIG. 1B. Here, an additional heat pump 135′ (e.g. thermo-electric heat pump) is used being thermally coupled in cascade fashion in between the heat pump 135 and heat sink 140 such that the cold side 132′ (first region from which heat is transferred) is thermally coupled (e.g. through heat spreader 138) to the hot side 134 (towards which the heat is transferred from cold side) of heat pump 135, and its hot side 134′ is coupled to the heat sink 140.